The present application claims priority based on the foreign application filed in France Serial No. 99 01782 on Feb. 15, 1999.
The aim of the invention is a packaging, a container or a containment system where the leakage rate must, if possible, be nil or remain very low. The invention is particularly applicable to transport or storage containers for radioactive products or toxic chemical products.
A storage or transport container for hazardous substances is shown in FIG. 1. This container comprises, in a known manner, an envelope 1 in steel for example. This envelope contains a mechanical and thermal protection 2 inside which is housed the containment in the chamber 3. This chamber is manufactured in a material suitable for containing the hazardous material to be stored. The containment is constituted by a tank 4 and a cover 5. In the same manner, the envelope 1 and the mechanical and thermal 2 part comprises a section protecting the tank 4 and a section protecting the cover 5. The cover 5 of the containment is generally constituted by a plug in which the seals are maintained. One of the gasket surfaces is integrated in the tank 4, the other is provided by the cover 5. The gasket surfaces are usually metal, for example in steel. In numerous containment systems, leaktightness is provided by two elastomer seals. The inter-seal volume, i.e. the volume contained between the two seals the cover 5 and tank 4 is used for measurement of the leakage rate. After filling the containment and its closure, the pressure can eventually be measured in the inter-seal space, by having for example previously emptied this volume and then filling with helium, and in this way check the leaktightness before definitive storage or the transport of the containment chamber. But subsequently, this pressure control device is not kept on the premises for reasons of pollution that the gas contained in the inter-seal space could cause in the event of leakage. On the other hand, leaktightness over a period of time is not guaranteed, as the seals can become porous, notably due to the air located in the inter-seal space or products contained in the chamber.
The invention involves a containment chamber which facilitates solving the two problems of the previous technologyxe2x80x94permanent control of leaktightness in the containment system and secondly, ensuring less wear and tear on the seals.
In order to continually measure the leakage rate of the leaktight chamber 3, a liquid is introduced in the inter-seal volume delimited by the cover, the tank and at least two seals. The liquid which occupies the inter-seal volume is part of the packaging leaktightness system by plugging possible small holes in the seals. Modification of a value of electrical quantities measured between the cover and the tank, which is variable depending on the quantity of liquid contained in the inter-seal volume, in this case facilitates determining a leakage value. When the cover 5 is put in place and tightened on the tank 4, the liquid is introduced by means of the first tap, for example. When the liquid has filled the inter-seal volume, the air bubbles and overflow of liquid is drained through the second tap. Closure of the two taps facilitates ensuring that the inter-seal volume is full of liquid. A leakage will be reflected by discharge of liquid and therefore by modification of the value of electrical quantities measured between the cover and the tank. In this way, taken in its most usual form, the invention is relative to a leaktight chamber comprising a tank having a cover surface to receive a cover, this cover surface itself comprising at least two gasket surfaces, leaktight seals inserted in the gasket surfaces of the tank, a cover having gasket surfaces, the leaktight seals being equally inserted in the said gasket surfaces of the cover, two seals, an inter-seal surface of the cover and an inter-seal surface of the tank, together delimiting an inter-seal volume, leaktight container characterized in that it comprises at least two means for connecting, reversibly, the inter-seal volume with an intake of fluid for one of the reversible means of connection with evacuation of fluid for the other means of reversible connection, and electrical coupling means to electrically connect the cover on the one hand and the tank on the other hand with outside measurement means.
In this way conveniently the invention provides continuous control of the leakage rate of the containment chamber.
In the preferred mode of execution, the means to place the inter-seal volume in communication in a reversible manner with an inlet and evacuation of fluid respectively are constituted by valves or taps.
The check on leaktightness is mainly provided by the interposition in the inter-seal space of a conductive liquid which facilitates electric continuity between the cover and the tank of the containment system. It is therefore sufficient, through appropriate means, to make a current circulate between the cover and the tank, and to measure continuously an electric quantity (amperage, resistance, etc.)xe2x80x94a shift in this quantity or a complete total variation (amperage becoming nil, resistance becoming infinite, etc.) will then be evidence of the disappearance of all or part of the liquid and therefore of leaktightness loss. In other words, a circuit is formed in which part is constituted by the conductive liquid in the inter-seal space which opens as soon as the liquid disappears from this volume. The type of this conductive liquid depends on the application. It should be pointed out that the inter-positioning of the liquid itself improves leaktightness, role of 3rd seal and possibility of improving resistance over time of the two other seals. Preferably, measuring means for the electrical quantity are coupled to alarm triggering devices, themselves connected to a visual or sound alarm.
The invention also concerns a process of leak detection of a leaktight containment comprising a tank, a cover and two seals tightened between the tank and the cover, delimiting an inter-seal volume, process typified in that:
one fills the inter-seal volume with a liquid, conductor of electricity;
an electric current is circulated between the tank and the cover;
the resistance or value of the current is measured in order to deduce a loss of quantity of conductive liquid contained in the inter-seal volume.